1. Field of the Invention
This invention relates to a method for removing organic contaminants from aqueous compositions, and is particularly useful in the treatment of bodies of water or process streams which are contaminated with organics.
2. Prior Art
One of the major problems facing cities, chemical manufacturers, and industries using various chemicals, is waste disposal. More particularly, cities and industries are often faced with the need to dispose of aqueous compositions containing organic contaminants. Regulations make it impossible to simply dump such waste water into streams, even if such method of disposal were otherwise desirable. Various methods have been proposed for removing such contaminants from waste water, but they have been relatively expensive or inefficient. Therefore, the removal of contaminants from aqueous compositions, and in particular from waste water containing small amounts of contaminants, is a problem which has not been completely solved.
There exist numerous methods for removing organic contaminants from aqueous compositions, typically oil and water emulsions; see for example the following relevant U.S. patents: U.S. Pat. No. 2,367,384 to Tymstra; No. 2,937,142 to Rios; No. 3,196,619 to Shock; No. 3,487,928 to Canevari; No. 3,528,284 to Skoglund et al; No. 3,986,953 to Beaucaire; No. 4,231,866 to Moser et al; and No. 4,279,756 to Weiss et al
More specifically, Tymstra describes a method for removing small quantities of water-immiscible organic oily impurities from water. The method consists of contacting the oily composition with an inert solid coated with a cation surface-active bonding agent. The solid employed may be beach sand, mud flat deposits, silt, clay, limestone, silica, rice hulls, etc. The cationic surface-active bonding agent may be quaternary ammonium, phosphonium, arsonium bases, or primary, secondary, or tertiary organic amines or salts thereof. This reference does not teach or suggest the use of the specific organoclays utilized herein to remove organic contaminants from aqueous compositions, nor the unexpected efficiencies of these clays.
Rios separates phenolic substances from aqueous solutions by contacting the aqueous solution with a clay adsorbent. The clay is previously treated by depositing carbonaceous material thereon, and then subjecting it to combustion regeneration to burn off the carbonaceous material.
Canevari separates droplets of oil from an aqueous phase, using a mixture comprising a sodium montmorillonite clay and an organic cationic agent or glycol. The organic cationic agent is preferably an amine. The mixture is applied as a flocculating clarifying solution containing from 1 to 5% of clay to water, and an effective amount of the organic cationic agent or glycol.
Beaucaire describes breaking an oil-water emulsion with waste-pickling acid solution, and thereafter converting the iron ions present in the waste-pickling solution to magnetite particles which absorb the oil. The magnetite particles and oil absorbed thereon are separated from the solution leaving a clarified solution.
Moser et al separates organic and aqueous phases by treatment of the emulsions with diatomaceous earth at an elevated temperature.
Weiss et al describes the use of a finely divided particulate mineral or clay material, the individual particles of which have been treated to produce a thin hydroxylated surface layer having a positive zeta potential at the adsorption pH.
None of the aforementioned references teach or suggest the use of the organoclays as in the present invention to remove organic contaminants from water.
Additionally, organoclays are well-known in the art, see for example the following U.S. patents: U.S. Pat. No. 2,531,427 to Hauser; No. 2,966,506 to Jordan; No. 3,422,185 to Kuritzkef; No. 3,974,125 to Oswald; No. 4,081,496 to Finlayson; and No. 4,105,578 to Finlayson et al
None of these aforementioned references teach or suggest the use of these organoclays to remove organic contaminants from water.
In my Ser. Nos. 307,300 and 419,303 applications methods are disclosed for removing organic contaminants from an aqueous composition contaminated therewith. The method in general comprises contacting the aqueous composition with a sufficient amount of organoclay for a sufficient amount of time to absorb a substantial portion of the contaminant, and to form an aqueous organoclay admixture. The organoclay and aqueous composition are then separated from each other. The method is particularly useful for separating oily contaminants from water and toxic substance precursors, e.g. humic acid and other toxic organics (e.g. PCB's) from water.
Furthermore, in my aforementioned Ser. No. 419,303 application a method is disclosed for breaking emulsions of an organic composition and water or polar fluids. The method comprises contacting the emulsion with an emulsion-breaking amount of an organoclay to adsorb a major portion of the organic composition. Subsequently, a portion of the organoclay or water may be removed.
The methods of my aforementioned applications, while extremely effective, are less than ideal where one desires to remove from aqueous systems organic contaminants which comprise low molecular weight substances such as trichloroethane, chloroform, dichloroethane, etc. which are relatively quite soluble in water. Thus for example, if a mixture of gasoline and water is passed through a column packed with organoclays in accordance with my earlier inventions, the lower molecular weight higher solubility components such as benzene will tend to pass too readily through the column, while the higher molecular weight, lower solubility components such as toluene and xylene, will be more thoroughly retained at the column.
It has long been known in the prior art that activated carbons are very effective in adsorbing organic contaminants, including both high and low molecular weight substances. Such materials may for example be so used by packing a column with activated carbon granules and passing the aqueous composition through the column.
On the other hand activated carbon has a serious limitation where used to remove high molecular weight contaminants and/or emulsified contaminants. Such components tend to rapidly foul the carbon. This is particularly true if the materials are emulsified in the water. Under those circumstances a film tends to form upon the granulated carbon particles, rendering access to the high surface area difficult or impossible in rapid fashion. Thus the carbon is of limited use or at least has a quite limited life, after which it must be regenerated by time-consuming and costly treatments.
It is also well known that the aforementioned low molecular weight compounds are very amenable to air stripping. In the case of air stripping, the higher molecular weight compounds and oil tend, however, to form gums on the surfaces of the air stripping towers, thus adversely effecting the performance of the air stripping unit.